This invention relates to optical communications and in particular to an assembly for maintaining optical communication between relatively movable members.
Many optical communications systems are nowadays used instead of conventional electrical communications systems in order to render the system immune from electromagnetic interference and at the same time to take advantage of the high bandwidth capabilities of optical signalling. Many applications require data to be transferred from a rotating to a stationary member (or vice versa) and whereas in conventional electrical systems this is accomplished by way of a slip-ring assembly which is relatively simple in construction known forms of the equivalent optical assembly are much more complicated. These known optical assemblies are described (for example) in U.K. patent specifications Nos. 1528251 and 2037979A and also in the Journals "Eureka" (June 1981 p. 47) and "Photonics Spectra" (February 1982, p. 41).
It is an object of the present invention to provide an improved form of assembly for maintaining optical communication between relatively movable members.
According to the present invention there is provided an assembly for maintaining optical communications between relatively movable members, comprising a housing mode of a low refractive index material and defining a hollow toroid shaped chamber and first and second passageways leading from said hollow toroid shaped chamber such that there is substantially stepless transition from said toroid shaped chamber in a clockwise direction into the first passageway and from the toroid shaped chamber in a counter-clockwise direction into the second passageway, said passageways and toroid shaped chamber being filled with a fluid of high refractive index whereby said assembly forms a light guide, wherein said housing is formed in two portions mounted for relative rotation about an axis perpendicular to the toroidal equatorial plane and coincident with the centre of the toroid shaped chamber, said portions having an interface lying on a surface of revolution generated about said axis, one portion incorporating said first passageway and the other portion incorporating said second passageway.
It will be understood that each passageway functions as a connector for receiving a fibre light guide and, in use, one housing portion is rigidly connected to one movable member with a fibre light guide extending therebetween whilst the other housing portion is rigidly connected to the other movable member with a fibre light guide extending therebetween so that relative rotation of said members effects relative rotation of said housing portions, the rotational axes being arranged appropriately.
Conveniently the bore of said passageways is the same as that of said toroid shaped chamber and the angle of inclination between the toroidal longitudinal axis and the longitudinal axes of said passageways, at least at that portion thereof adjusting the toroid, is as small as possible. With this arrangement the coupling losses between the toroid and the passageways is minimised and where the overall diameter of the toroid is substantially greater than the diameter of the fibre light guides connected to the passageways the loss between light fed to the assembly through one passageway and extracted from the assembly through the other passageway can be as little as 3 dB.
Conveniently said housing material is mouldable and both housing portions (and pertaining passageway) are identical geometrically so that only a single mould is required to produce two housing portions which can be arranged to form said assembly. It will be appreciated that with this arrangement the surface of revolution requires to be coincident with the toroidal equatorial plane.
Conveniently said passageways have bores of circular cross-section. This cross-section may be constant throughout the length of the passageway but alternatively the bores may be tapered such that the circular cross-section diminishes or increases towards the toroid.
Preferably said passageway terminates at its end remote from the toroid with an internal shoulder to form a seat for the optical fibre to be fitted thereto whereby coupling loss between the passageway and the fibre can be minimised.
In order to provide a fluid seal at the interface between the housing portions a lip seal may be provided on one portion or each portion may be provided with flanges on the surface of revolution such flanges being provided with mating circular grooves and recesses forming a rubbing seal for containment of fluid within the housing but since such an arrangement is extremely difficult to manufacture to the high degree of accuracy required to avoid optical degradation of the assembly it is preferred, in order to effect the same result, to accommodate the entire assembly in a canister containing the same fluid as is within the toroid (or a fluid compatible therewith). The fluid outside the assembly may be pressurised, for example, by gravity.
By way of example the housing may be made of an acrylic plastics material and the fluid may be a polyphenyl ether such as SANTOVAC 5 (made by Monsanto Chemicals, Inc.).